#64 Can only open image files from within GIMP

In OS X Lion, I cannot open any image file in GIMP 2.8.4 from within the Finder.
If I double-click an XCF image, right-click an image and choose "Open with -> GIMP", or if I drag it onto the GIMP icon in the dock or in the Finder, GIMP displays a message saying it cannot open files in that format. I need to open the file from within GIMP itself with the "Open" menu.